U.S. patent number 4,442,901 [Application Number 06/355,478] was granted by the patent office on 1984-04-17 for landfill gas recovery method.
This patent grant is currently assigned to Getty Synthetic Fuels, Inc.. Invention is credited to Stanley W. Zison.
United States Patent |
4,442,901 |
Zison |
April 17, 1984 |
**Please see images for:
( Certificate of Correction ) ** |
Landfill gas recovery method
Abstract
A method of collecting landfill gas from a landfill comprising
providing a porous collector in the landfill having a relatively
broad collection zone in the path of migrating landfill gas,
controlling the pressure in the collector to induce the landfill
gas near the collector to flow into the collector, removing the
landfill gas from the collector, and substantially excluding air
from the atmosphere from entering the collector when the collector
is collecting landfill gas.
Inventors: |
Zison; Stanley W. (Irvine,
CA) |
Assignee: |
Getty Synthetic Fuels, Inc.
(Signal Hill, CA)
|
Family
ID: |
23397561 |
Appl.
No.: |
06/355,478 |
Filed: |
March 8, 1982 |
Current U.S.
Class: |
166/369;
166/50 |
Current CPC
Class: |
E21B
43/305 (20130101); E21B 43/00 (20130101); B09B
1/00 (20130101); Y02W 30/30 (20150501); Y02W
30/35 (20150501) |
Current International
Class: |
B09B
1/00 (20060101); E21B 43/30 (20060101); E21B
43/00 (20060101); E21B 043/22 () |
Field of
Search: |
;166/50,369,370,278
;405/128,129 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Methane Gas Recovery from Landfills Turns This . . . Into This",
by Southern California Gas, PG&E, and Argonne National
Laboratory..
|
Primary Examiner: Novosad; Stephen J.
Assistant Examiner: Neuder; William P.
Attorney, Agent or Firm: Peterson; Gordon L.
Claims
I claim:
1. A method of collecting landfill gas from a landfill wherein the
landfill gas is produced by refuse in the landfill and migrates
upwardly toward the upper surface of the landfill, said method
comprising:
providing a porous collector near the upper surface of the landfill
with the collector including a network of apertured conduits and
having a relatively broad collection zone in and generally
transverse to the path of the migrating landfill gas;
placing the collector at a pressure so that at least substantial
quantities of the landfill gas in said path are induced to flow
into the collector;
removing the landfill gas from the collector; and
substantially preventing air from the atmosphere from being drawn
into the landfill gas-producing refuse when the collector is
collecting landfill gas.
2. A method as defined in claim 1 wherein said collection zone
faces generally downwardly.
3. A method as defined in claim 1 wherein said step of providing
includes providing said collector within twelve feet of the top of
the refuse in the landfill.
4. A method as defined in claim 1 wherein said step of providing
the porous collector includes providing aggregate in the path of
the migrating landfill gas with the aggregate defining flow
passages between adjacent aggregate particles.
5. A method as defined in claim 1 including conducting at least the
combustible portion of the landfill gas to a location for marketing
such portion as useful fuel.
6. A method as defined in claim 1 wherein said step of placing
includes controlling the pressure in the collector to at least
assist in avoiding drawing oxygen from the atmosphere into the
landfill gas-producing refuse when the collector is collecting
landfill gas.
7. A method as defined in claim 1 wherein said step of preventing
includes providing a gas barrier above the collection zone.
8. A method as defined in claim 7 wherein said step of providing a
gas barrier includes providing a broad sheet of plastic above the
collection zone.
9. A method as defined in claim 7 wherein said step of providing a
gas barrier includes providing a layer of polymerized clay above
the collection zone.
10. A method as defined in claim 7 wherein the gas barrier extends
laterally beyond the periphery of the collector.
11. A method as defined in claim 1 wherein said step of providing
includes providing said collector near the upper surface of the
refuse in the landfill and said step of preventing includes
controlling the pressure in the collector to at least assist in
avoiding drawing oxygen from the atmosphere into the landfill
gas-producing refuse when the collector is collecting landfill gas
and providing a gas barrier above the collection zone.
12. A method of collecting landfill gas from a landfill wherein the
landfill gas is produced by decomposition of refuse in the landfill
and migrates upwardly toward the upper surface of the landfill,
said method comprising:
surveying the landfill to establish gas venting rates for a
plurality of regions adjacent the upper surface of the
landfill;
providing a porous landfill gas collector in the landfill near the
upper surface of the refuse in the landfill and near one of said
regions having approximately the desired gas venting rate;
placing the collector at a pressure to induce landfill gas adjacent
the collector to enter the collector;
removing the landfill gas from the collector; and
substantially preventing oxygen from the atmosphere from entering
the refuse which is producing landfill gas when the collector is
collecting landfill gas.
13. A method as defined in claim 12 wherein at least some of said
regions are on the upper surface of the landfill.
14. A method as defined in claim 12 wherein said one region has a
gas venting rate which is above average for those regions surveyed
and said collector is at said one region.
15. A method as defined in claim 12 wherein said collector is
within twelve feet of the top of the refuse in the landfill.
16. A method as defined in claim 12 wherein said collector includes
a network of apertured conduits defining a broad collection zone
which is oriented generally transverse to the path of migrating
landfill gas.
17. A method as defined in claim 12 wherein said step of preventing
includes controlling the pressure in the collector to at least
assist in avoiding drawing oxygen from the atmosphere into the
collector when the collector is collecting landfill gas.
18. A method as defined in claim 12 wherein said step of preventing
includes providing a gas barrier above the collection zone.
19. A method of making a landfill gas recovery well in a landfill
wherein the landfill gas is produced by decomposition of refuse in
the landfill and migrates upwardly toward the upper surface of the
landfill, said method comprising:
surveying the landfill to establish gas venting rates for a
plurality of regions adjacent the upper surface of the
landfill;
providing a broad, shallow hole near one of said regions with the
hole extending downwardly at least to the upper surface of the
refuse in the landfill;
installing a porous landfill gas collector near the upper surface
of the refuse in the hole adjacent the bottom of the hole with the
collector having a relatively broad collection zone generally
transverse to the migrating landfill gas for collecting at least
some of such landfill gas;
installing a gas barrier in the hole above the collector;
at least partially filling the hole to cover the gas barrier;
and
providing a landfill gas recovery conduit which extends from the
collector whereby landfill gas entering the collector can be
recovered.
20. A method as defined in claim 19 wherein said step of providing
includes excavating a region of the landfill to provide said
hole.
21. A method as defined in claim 19 wherein said step of installing
the collector includes installing a network of apertured
conduits.
22. A method as defined in claim 21 wherein said conduits are in
the refuse and extend more horizontally than vertically.
23. A method as defined in claim 19 wherein said step of installing
a gas barrier includes installing a layer of polymerized clay above
the collector with a layer of refuse being between the barrier and
the collector.
24. A method as defined in claim 23 wherein said step of installing
the collector includes installing a network of apertured conduits
which extend generally laterally within the hole.
25. A method as defined in claim 19 wherein said step of installing
the collector includes partially filling said hole with aggregate
with the aggregate being in contact with the refuse.
26. A method as defined in claim 19 wherein said step of installing
the barrier includes providing a flexible sheet which is
substantially impervious to landfill gas and a protective layer
adjacent the sheet to protect the flexible sheet against
perforation.
27. A method as defined in claim 19 including providing the
collector with increased landfill gas carrying capacity adjacent
the landfill gas recovery conduit.
28. A method of collecting landfill gas from a landfill wherein the
landfill gas is produced by decomposition of refuse in the landfill
and migrates upwardly toward the upper surface of the refuse, said
method comprising:
surveying the landfill to establish gas venting rates for a
plurality of regions adjacent the upper surface of the
landfill;
installing a porous landfill gas collector near the upper surface
of the refuse in the landfill and near one of said regions with the
collector being in the path of the migrating landfill gas and
having a relatively broad collection zone generally transverse to
the migrating landfill gas;
installing a gas barrier above the collector;
placing the collector at a pressure to induce at least some of the
landfill gas in said path to flow into said collector; and
removing the landfill gas from the collector.
29. A method as defined in claim 28 wherein said step of placing
includes controlling the pressure in the collector to at least
assist in avoiding drawing oxygen from the atmosphere into the
collector when the collector is collecting landfill gas.
30. A method as defined in claim 1 wherein the landfill has an
upper preexcavation surface and the broad dimensions of the
collection zone are generally parallel to said upper preexcavation
surface of the landfill.
31. A method as defined in claim 1 wherein said collector provides
a large number of apertures spread over the broad collection zone.
Description
BACKGROUND OF THE INVENTION
The decomposition of refuse in a landfill produces landfill gas
which may include, for example, about fifty (50%) percent methane.
Landfill gas within the landfill is at some positive pressure,
i.e., pressure above ambient, and accordingly, the landfill gas
tends to migrate vertically toward the surface of the landfill due
to the differential pressure between the interior of the landfill
and the atmosphere. Initially, landfill gas escaping from the
surface of a landfill was considered hazardous because of its
methane content. However, more recently, landfill gas has been
recovered and its nonmethane components removed to varying degrees
to permit it to be used as an energy source.
The common technique for recovering landfill gas for ultimate
utilization is to drill a vertical well, the depth of which may be,
for example, from thirty (30) feet to about 250 feet. The well is
lined with a perforated casing so that landfill gas can enter the
well through the perforations. To induce landfill gas to flow into
the well, the well is maintained at below local landfill
pressure.
When landfill gas is to be recovered for ultimate utilization, it
is important to exclude oxygen from the landfill because oxygen is
detrimental to the production of methane by the landfill.
Accordingly, it is important that the pressure within the well not
be allowed to get so low that ambient air is drawn into the
landfill through the surface of the landfill. This limitation on
the negative pressure within the well limits the zone of influence
which each vertical well has, and this is discussed, for example,
in Johnson et al U.S. Pat. No. 4,026,355.
The traditional vertical well has a number of significant
disadvantages. For example, if breakthrough, i.e., the drawing of
oxygen into the landfill, occurs, there may be a significant time
lag between the occurrence of breakthrough and its discovery. Also,
when breakthrough occurs, it may be difficult to find the source of
the breakthrough at the surface. Boring of vertical wells can be
difficult particularly under wet conditions, and the depth of
vertical wells is a significant hazard. Leachate tends to collect
in the bottom of vertical wells and must be pumped out, and access
to the lower regions of the vertical well is difficult to obtain.
Finally, the lateral movement or shearing of adjacent planes in the
landfill can cause the well to fail in shear.
SUMMARY OF THE INVENTION
This invention is based, in part, upon the recognition that the gas
generation rate is substantially equal to the venting rate. In
other words, almost all of the landfill gas that is generated must
vent to the atmosphere through the upper surface of the landfill.
This is the result of the differential pressure between the
interior of the landfill and ambient air pressure.
This invention takes advantage of this fact and provides for
collection of the landfill gas in broad, shallow wells. Because
substantially all of the landfill gas that is generated finds its
way to the surface on its own, this invention eliminates the deep
vertical well of the prior art and its accompanying problems and
provides for landfill gas collection near the surface of the
landfill.
With this invention, a porous collector is provided in the landfill
in the path of landfill gas migrating to the surface. The interior
of the collector is placed at a pressure that will induce the
landfill gas in the vicinity of the collector to flow into the
collector. The collected landfill gas is then removed from the
collector.
The collector preferably has a relatively broad collection zone
which may be panel-like. This provides the collection zone with two
substantial dimensions, i.e., a broad collection surface or area
whereas the single vertical well provides essentially a collection
line. The broad collection zone is preferably oriented generally
transverse to the path of migrating landfill gas, whereas the
collection line of the single vertical well is oriented
vertically.
The porous collector may be of various different constructions and
may include, for example, aggregate such as gravel. Alternatively
or in addition thereto, the collector may include one or more
apertured conduits. In one preferred construction, a network of
apertured conduits is utilized for landfill gas collection
purposes.
Oxygen may be substantially excluded from the collector and
landfill in different ways. For example, to collect the landfill
gas migrating to the surface along a path lying directly beneath
the collector, the collector is placed at least at atmospheric
pressure when the landfill gas enters it. In this event, landfill
gas in this path is induced to enter the collector, and there is no
differential pressure between the landfill surface and the
collector that would tend to cause breakthrough.
To increase the horizontal dimensions of the region from which
landfill gas is drawn into the collector, a gas barrier may be
installed above the collector. This permits the pressure within the
collector to be at less than atmospheric thereby tending to induce
flow of landfill gas into the collector from regions radially
outward from the collector. The gas barrier may be coextensive
with, or extend radially outwardly beyond, the collector.
Although the collector can be located at different depths within
the landfill, it is preferably near the upper surface of the refuse
in the landfill. By positioning the collector near the upper
surface of the refuse in the landfill, excavation is minimized,
access to the collector is facilitated and the region in which
breakthrough may occur is minimized. If breakthrough occurs, oxygen
will be introduced only into the upper region of the landfill.
Additionally, a maximum amount of water vapor can condense out of
the landfill gas and be retained by the landfill before it enters
the collector. Because the collector is located at a shallow
location, if breakthrough occurs, the time lag between when it
occurs and when it is observed is significantly less than for a
deep well. Also, water can drain from a shallow well into the
landfill, and there is no shearing problem with a shallow well.
The gas barrier may comprise one or more layers of any suitable
material which is substantially impervious to landfill gas and
oxygen. For example, the gas barrier may include a thin plastic
sheet and/or a polymerized clay, such as polymerized bentonite.
Regardless of the type of gas barrier used, as the generation rate
of the well declines, its surface area can be extended to provide
additional gas inflow rather than adding additional wells. Also, it
is not necessary that the gas barrier be totally impervious to gas
flow because the area of the gas barrier will be quite large and so
cracks or perforations in the barrier will typically represent only
a very small percent of the total surface area of the barrier.
The landfill gas generation rate is not uniform throughout the
landfill. Moreover, because the landfill is not homogeneous, the
flow of landfill gas to the surface is also not homogeneous.
Accordingly, one problem with landfill gas recovery is determining
where to put the wells. For deep vertical wells, it is sometimes
necessary to extensively sample the landfill at various depths in
an effort to determine the best locations for the deep wells.
With this invention, landfill surveying is made easier, and wells
can be positioned at more desirable locations. Because the landfill
gas is collected near the landfill surface, the landfill is
surveyed to determine the gas venting rates for a number of regions
at or adjacent the upper surface of the landfill. The collector is
then located at or near the region having approximately the desired
gas venting rate.
This invention, together with additional features and advantages
thereof, may best be understood by reference to the following
description taken in connection with the accompanying illustrative
drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a plan view, with portions broken away, of a landfill
having a shallow well constructed in accordance with the teachings
of this invention in the landfill.
FIG. 2 is a sectional view taken generally along line 2--2 of FIG.
1.
FIG. 3 is a plan view, with portions broken away, of a portion of a
landfill having a second form of shallow well constructed in the
landfill.
FIG. 4 is a sectional view taken generally along line 4--4 of FIG.
3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 and 2 show a portion of a landfill 11 having a shallow well
13 therein. The landfill 11 includes refuse 15 which may, for
example, be over 200 feet deep and a layer of cover material 17
above the refuse. The refuse 15 decomposes and produces a landfill
gas which is under some small positive pressure greater than
ambient. Consequently, the landfill gas migrates upwardly toward
the upper surface 19 of the landfill. The shallow well 13 is
located in the path of some of the landfill gas which is migrating
upwardly toward the upper surface 19.
Although the shallow well 13 could be located virtually anywhere in
the landfill, it is generally preferred to locate the well 13 for
maximum production of landfill gas. To accomplish this, the
landfill 11 is surveyed to determine the gas venting rate at
various regions of the landfill. Because the well 13 is shallow,
the gas venting rate may be determined for various regions on the
upper surface 19 or at shallow regions beneath the upper surface
19, such as at the upper surface 21 of the refuse 15. Determining
the venting rate at the surface 19 has the advantage of not having
to excavate to perform the tests and it provides venting rate
information very close to where actual collection of the gas will
occur.
The gas venting rate can be determined in accordance with various
known techniques. For example, landfill gas has an odor and so
relative gas venting rates can be determined by smelling with the
more odiferous regions being regions where the gas venting rate is
higher.
Another way to determine the gas venting rate is to use a
methanometer. For this purpose, a flux box having an open bottom is
placed on the surface at which it is desired to determine the gas
venting rate, and the landfill gas is allowed to flow into the flux
box. The methanometer then provides a read-out indicative of the
landfill gas venting rate.
After the survey of gas venting rates has been completed, the
shallow wells 13 are located at the regions having the desired
landfill gas venting rates. Typically the regions selected for one
of the wells 13 will have an above-average landfill gas venting
rate for those regions surveyed, and wells may be located at the
regions having the maximum gas venting rates.
After the site for the shallow well 13 has been selected, the cover
material 17 is excavated from the selected region of the landfill
11 to form a hole 23. In the embodiment of FIGS. 1 and 2, the hole
23 extends to approximately the upper surface 21 of the refuse 15.
Although the hole 23 may cover any desired area of the landfill as
viewed in plan, preferably it covers a broad panel-like region so
that it has a relatively broad area in the path of landfill gas
migrating toward the upper surface 19. For example, the hole 23 may
be 150 feet.times.150 feet as viewed in plan.
The depth of the hole 23 is preferably to approximately the upper
surface 21 of the refuse 15. Although the hole 23 could be deeper
and penetrate the refuse 15 to varying degrees, there appears to be
no significant advantage to this and so it is generally preferred
to have the bottom of the hole be closely adjacent the upper
surface 21 of the refuse 15 in the embodiment of FIGS. 1 and 2. As
a rule of thumb, which is not critical, it generally is unnecessary
to make the hole 23 any more than 12 to 15 feet deep.
Next, a porous collector 25 is installed in the hole 23. In this
embodiment, the collector 25 includes aggregate 27 and a network of
apertured conduits comprising four apertured conduits 29 which, for
example, may be arranged perpendicular to each other to form a
cross as shown in FIG. 1. The particles of the aggregate 27 must be
of sufficient size to permit adjacent aggregate particles to form
passages so that the body of aggregate forms a porous mass. For
example, the aggregate 27 may be gravel, broken concrete or the
like.
As viewed in plan, the aggregate 27 preferably covers the entire
length and width dimensions of the hole 23. Accordingly, the
passages formed by the aggregate 27 can receive landfill gas from
at least the area immediately therebelow. Thus, the aggregate 27
provides a broad panel-like collection zone facing downwardly and
extending transverse to the path of the migrating landfill gas. The
broad collection zone has a large number of apertures spread
throughout to receive the migrating landfill gas. To maximize
collection, the broad dimensions of the collection zone are
generally parallel to the preexcavation upper surface 19 which may
be horizontal or inclined.
The conduits 29 are centrally located in the hole 23 and in the
aggregate 27. As described more fully hereinbelow, the interiors of
the conduits 29 are preferably maintained at a pressure less than
the pressure of the landfill gas in the refuse adjacent the
aggregate 27. Accordingly, the landfill gas is induced to flow into
the aggregate 27 and toward the conduits 29. This means that more
landfill gas exists centrally in the collector 25 than around its
periphery. Accordingly, in the form shown in FIG. 1, the aggregate
has a greater thickness centrally of the collector 25 than at the
periphery of the collector. In the specific embodiment shown in
FIGS. 1 and 2, the thickness of the aggregate 27 progressively
increases from the periphery toward the center of the collector
25.
Any number of the conduits 29 may be employed, and the four
conduits illustrated are purely illustrative. The conduits 29 may
be substantially shorter than the length and width dimensions of
the aggregate 27. By way of example and not by way of limitation,
each of the conduits 29 may be twenty feet in length when used in a
150 foot square hole 23. Although it is not critical, the conduits
29 in the embodiment illustrated are of equal length, extend
horizontally and parallel to the upper surface 21, and are spaced
upwardly from the upper surface 21 of the refuse 15. The conduits
29 have their outer ends capped and may be constructed of any
suitable metal or plastic; however, polyethylene is preferred. The
size, arrangement and configuration of the apertures in each of the
conduits 29 may be varied, however, a large open area is
preferred.
The conduit 29 is coupled to a landfill gas recovery conduit 31
which is coupled to the inner ends of the conduits 29. The conduit
31 may extend to a location above the upper surface 19. The end of
the conduit 31 remote from the conduits 29 is connected to a
suitable vacuum source, such as a vacuum pump 33 so that the
pressure within the conduits 29 and 31 can be controlled and
preferably maintained slightly negative, such as, for example, two
inches of water less than current ambient pressure.
In installing the collector 25, a first portion of the aggregate 27
can be placed in the hole 23. Thereafter, the conduits 29 and 31
can be installed with the conduits 29 resting on top of this first
layer of aggregate. Thereafter, the remainder of the aggregate 27
can be filled into the hole 23 to completely cover the conduits
29.
To increase landfill gas production from the well 13 without
drawing air from the atmosphere into the landfill, a gas barrier 35
can be employed. In this embodiment, the gas barrier 35 is in the
form of an imperforate polyethylene sheet which is above the
collector 25. The gas barrier 35 covers at least the region
immediately above the collector. If desired, the gas barrier 35 may
extend laterally beyond the periphery of the collector. The conduit
31 extends upwardly through the gas barrier 35, and the gas barrier
is otherwise imperforate. To protect the gas barrier 35 from being
punctured by any sharp components either above or below the barrier
35, the barrier is preferably sandwiched between protective layers,
such as sand 37 and 39 which are coextensive with the gas
barrier.
Finally, the hole 23 is filled with soil 41. If desired, additional
soil may be piled on top to increase the thickness of the cover
layer beyond the thickness of the cover layer elsewhere in the
landfill 11.
In operation, the vacuum pump 33 is operated and controlled to
control the pressure in the collector 25 so that substantial
quantities of the landfill gas immediately beneath the collector
and in a peripheral zone outside the area of the collector are
induced to enter the collector and flow through the collector and
the landfill gas recovery conduit 31. If desired, the landfill gas
may then be conducted through a purification plant where the
desired quantities of impurities, i.e., non-methane components of
the landfill gas, are removed. The output from the purification
plant 43 constitutes sales gas which can be sold as useful
fuel.
The gas barrier 35 prevents any of the landfill gas entering the
collector 25 from escaping directly upwardly to the upper surface
19. In addition, the gas barrier 35 prevents oxygen from the air
immediately above the collector 25 from being drawn into the
collector or the landfill 11. The gas barrier 35 also permits a
somewhat higher vacuum to be applied to the collector 25 so that
landfill gas from a region of the landfill surrounding the
collector 25 is induced to flow into the collector, and this
increases the production of the well 13.
To illustrate the shallow nature of the well 13, the depth of the
collector 25 in a central region may be, for example, three feet.
The layers 37 and 39 and the gas barrier 35 may each be about one
foot thick, and there may be three feet of the soil 41 at the
central region of the well. Thus, in this example, the depth of the
well is only seven feet. Of course, the well 13 can be at any
desired depth, and the dimensions given herein are purely
illustrative.
FIGS. 3 and 4 show a shallow well 13a in the landfill 11 which is
identical to the shallow well 13 of FIGS. 1 and 2 in all respects
not shown or described herein. Portions of the well 13a
corresponding to portions of the well 13 are designated by
corresponding reference numerals followed by the letter "a."
The primary differences between the wells 13 and 13a are in the
construction of the collectors and the gas barriers. The well 13a
is the presently preferred embodiment of the invention because it
is less costly to construct.
The well 13a has a collector 25a which does not include aggregate.
Rather, the collector 25a includes a network of apertured conduits
which is much more extensive than the conduits 29 of FIGS. 1 and 2.
With the collector 25a, the apertured conduits extend to
substantially all areas of the hole 23a so that a broad panel-like
collection zone is provided by the conduits and such zone is
generally transverse to the path of the landfill gas migrating to
the upper surface 19a.
There are a large number of configurations which the network of
apertured conduits can assume. For example, the network of
apertured conduits may include a collection header 45 having its
ends capped and a series of parallel laterals 47 extending
perpendicular to the header and having their outer ends capped. The
header 45 and the laterals 47 may each be a polyethylene pipe, and
the header is of much larger diameter than the laterals. The header
45 may be substantially imperforate, whereas each of the laterals
47 is apertured and may have a relatively high percent of open area
to provide a large number of apertures spread over a broad zone
which is transverse to the direction of the migrating landfill gas.
The laterals 47 should be close enough together so that they can
collect substantially all of the landfill gas that flows upwardly
from the landfill immediately therebelow. For example, the laterals
47 may have a three foot center-to-center spacing. Although
different orientations are possible, in the embodiment illustrated,
the header 45 and the laterals 47 extend generally parallel to the
surface 19.
Another difference between the illustrated exbodiments of this
invention is that the collector 25a is preferably located slightly
below the upper surface 21a of the refuse 15a. For example, the
header 45 and the laterals 47 may be a few inches to a few feet
below the upper surface 21a. Of course, the collector 25a could be
placed at other depths in the landfill if desired.
Another difference between the illustrated embodiments of this
invention is that the gas barrier 35a is in the form of a layer of
polymerized clay, such polymerized bentonite. Polymerized bentonite
is available, for example, from Dowell (a division of Dow Chemical)
of Denver, Colorado, as Dowell M179 and is a known gas barrier.
The gas barrier 35a may be of any desired thickness and, in the
embodiment illustrated, lies on the surface 21a of the refuse 15a
with the refuse between the collector 25a and the barrier 35a
protecting the header 45 and the laterals 47. In this embodiment,
the gas barrier 35a extends laterally beyond the ends of the
laterals 47 as shown in FIG. 4, but this is not necessary.
The layer of soil 41a may be substantially uniform in thickness.
The landfill gas recovery conduit 31a is coupled to the header 45
and projects upwardly through the gas barrier 35a and the soil
41a.
In constructing the well 13a, the cover material 17a is removed and
either the entire top layer of the refuse 15a is removed or
trenches are dug in the refuse in a pattern appropriate to receive
the header 45 and the laterals 47. The collector 25a and the
conduit 31a are then installed, and the collector is buried in
refuse. Thereafter, the gas barrier 35a is constructed following
the directions of the manufacturer of the polymerized bentonite.
For example, the bentonite with additives, which can be purchased
in powdered form, is disked into the soil above the refuse 15a and
then the resulting mixture is drenched with water to bring about
the polymerization. The collector 25a and the conduit 31a are
subjected to pressures less than atmospheric during the curing of
the barrier 35a to prevent landfill gas from flowing through the
barrier as it is curing. If landfill gas were allowed to flow
through gas barrier 35a, the gas barrier would be porous as a
result of the passages established by the landfill gas. Lastly, the
soil 41a is placed into the hole 23a.
The well 13a is also shallow. For example, the collector 25a may be
under one foot of refuse. The gas barrier 35a may be one foot
thick, and the soil layer 41a may be three feet thick. Of course,
these dimensions, as well as other dimensions set forth herein, are
purely illustrative and should not be regarded as limiting the
invention in any way. The well 13a can be operated in the same
manner as described above for the well 13 to recover landfill gas
directly for use or for purification by a purification plant 43a to
produce sales gas.
Although exemplary embodiments of the invention have been shown and
described, many changes, modifications and substitutions may be
made by one having ordinary skill in the art without necessarily
departing from the spirit and scope of this invention.
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